The present invention relates to a dialyzing system and an operating method thereof. More particularly, the present invention relates to an improved dialyzing system of the kind wherein waste products are removed and ultrafiltration is performed from the blood by allowing the blood to come into contact with a dialysate across semi-permeable membranes, and to a method for advantageously operating such a dialyzing system.
Recently, various kinds of blood purification have been developed and put into practical use to perform treatment of end-stage renal failure patients by purifying the blood drawn from the patient""s body and returning the purified blood to the patients"" body. For this end, there have been widely used a dialyzing system, which generally comprises a dialyzer adapted to allow a blood and a dialysate, which flow into the dialyzer and flow out from the same through a blood flow line and a dialysate flow line, respectively, to be brought into contact with each other across semi-permeable membranes (i.e., dialysis membranes) such as hollow fiber membranes of cellulose, cuprammonium rayon, polysulfone, polyacrylonitrile or the like; and an ultrafiltration unit for regulating inflow and outflow rates of the dialysate entering into and discharging from the dialyzer through the dialysate flow lines.
In such a dialyzing system, the blood fed into the dialyzer is brought into contact with the dialysate fed into the dialyzer across the semi-permeable membrane in the dialyzer, thereby performing removal of waste products from the blood under the action of diffusion due to concentration gradients between the blood and the dialysate. On the other hand, excess water is removed from the blood through the semi-permeable membrane by ultrafiltration developing due to increase in the outflow rate of the dialysate from the dialyzer compared to the inflow rate of the dialysate to the dialyzer. The ultrafiltration unit regulates the inflow and outflow rates of the dialysate to and from the dialyzer.
In general, when purifying the patient""s blood with a dialyzing system, it is essential for safe extracorporeal circulation of the patient""s blood to take all sorts of expeditious measures in response to fluctuation in a pressure of the blood returning the patient""s body. For this end, such a dialyzing system is generally adapted to monitor such fluctuation in pressure in the blood flow line through a pressure-detecting line. This pressure-detecting line is connected at one end to an air chamber arranged in the blood flow line downstream of the dialyzer and at the other end to a pressure transducer. Moreover, an air filter is arranged in the pressure-detecting line. Thus, the pressure in the blood flow line downstream of the dialyzer is directly detected through the pressure-detecting line.
The above conventional dialyzing system, however, has serious problems such that an inner wall of the pressure-detecting line, the pressure transducer and/or air filter are polluted with the blood flowing into the pressure-detecting line whenever air leakage takes place at the connecting portion of the pressure-detecting line and the pressure transducer due to loosening of engagement. Since it is general practice to use the pressure transducer and the air filter repeatedly and since perfect cleaning, sterilization or disinfection of these members is difficult because of their complex structures, patients treated with such dialyzing system are exposed to high risks for various infectious diseases.
Therefore, before operating a conventional dialyzing system, it is needed to carefully inspect the pollution of the pressure transducer and the air filter arranged in the pressure-detecting line. If any pollution is found in these members, sufficient disinfectious treatment must be immediately made, and such treatment makes the operation of dialyzing system troublesome.
It is therefore an object of the present invention to provide an improved dialyzing system, which makes it possible to monitor the fluctuation of a pressure in the blood flow line in a convincing way which is free from the blood flow line.
Another object of the present invention is to provide a method of advantageously operating such a dialyzing system.
The present invention is based on the following two findings; the pressure of the blood in the central part of the dialyzer is equal to the pressure of the dialysate when dialysis is performed without any ultrafiltration, and a pressure in the specified site of the blood flow line, such as the air-blood chamber arranged in the blood flow line downstream of the dialyzer, is related to the pressure of the blood in the central part of the dialyzer. This makes it possible to determine a pressure of the blood in the specified site of the blood flow line from the pressure of dialysate detected when the ultrafiltration is stopped during dialysis.
According to the present invention, these objects are achieved by providing a dialyzing system comprising:
a dialyzer;
an ultrafiltration unit with which ultrafiltration is performed from the blood through semi-permeable membranes in the dialyzer by regulating an outflow rate of a dialysate from the dialyzer to become greater than an inflow rate of the dialysate to the dialyzer; and
a pressure-detecting means arranged in a dialysate flow line to detect a pressure of the dialysate;
wherein said system is adapted to determine a pressure in a blood flow line on the basis of the pressure of the dialysate detected by the pressure-detecting means at the time of temporary stop of ultrafiltration due to temporary stop of the operation of the ultrafiltration unit.
Since the dialyzing system of the present invention has need not to provide a pressure-detecting line for detecting the pressure in the blood flow line. Thus, there is no chance of leakage of the blood from the blood flow line associated with the leakage at the connecting portion of the pressure-detecting line and the pressure transducer, which would often occur when the pressure in the blood flow line is directly measured through the pressure-detecting line. As a result, inspecting steps for the pollution of the apparatus by blood prior to the operation of the dialyzing system become unnecessary, and the time and labor spent for such inspection can be eliminated.
In a preferred embodiment of the dialyzing system according to the present invention, the pressure in the blood flow line is determined by a control system on the basis of the dialysate pressure continuously detected during ultrafiltration and a difference between the dialysate pressure detected at the time of temporary stop of the ultrafiltration and the dialysate pressure just stabilized after the subsequent resumption of the ultrafiltration.
The difference between the dialysate pressure detected when ultrafiltration is temporarily stopped and the dialysate pressure just stabilized after subsequent resumption of the ultrafiltration is substantially equal to the difference between the blood pressure and the dialysate pressure measured when ultrafiltration is developing (i.e., transmembrane pressure). Therefore, in the present invention, the blood pressure in the dialyzer when ultrafiltration is developing is continuously monitored by adding the difference between the dialysate pressure detected when ultrafiltration is temporarily stopped and the dialysate pressure detected when a steady state is just reached after resumption of ultrafiltration to the dialysate pressure at any given time during ultrafiltration.
In a preferred embodiment of the present invention, such temporary stop of ultrafiltration is done at certain time intervals and/or whenever the ultrafiltration rate is changed.
Thereafter, the dialysate pressure is measured at the point in time the dialysate pressure is just stabilized after the resumption of ultrafiltration, so as to calculate the difference between the dialysate pressure detected at the time of temporary stop of ultrafiltration and the dialysate pressure thus-measured just stabilized after the resumption of the ultrafiltration. Thus, even after the ultrafiltration rate is optionally changed, a correct pressure of the blood in the dialyzer can be continuously monitored and/or displayed.
The dialyzing system further may include monitoring means and/or display means which directly or indirectly monitors and/or displays the pressure in the blood flow line determined by the control system. The provision of such monitoring or displaying means contributes to improve usability of the dialyzing system advantageously, which in turn ensures safer purification of the blood.
Preferably, the dialyzing system is adapted to monitor and/or display a pressure of blood at a specified site of the blood flow line. Such pressure of the blood at a specified site of the flow line is determined on the basis of the detected pressure of the dialysate and a pressure gradient from the central part of the dialyzer to the specified site, which is calculated from a flow resistance of the blood flow line and the blood flow rate.
Therefore, the dialyzing system of the present invention can be advantageously operated while reliably monitoring the pressure at an optional site in the blood flow line without any risk for leakage of blood from the blood flow line or any problem caused thereby, such as the pollution of the dialyzing system due to contact with the leaked blood, or any increase in the number of steps of disinfection and inspection of the dialyzing system in terms of pollution by the leaked blood. As a result, the extracorpreal circulation of the patient""s blood and the purification thereof can be efficiently carried out in more safety.
According to the present invention, the dialyzing system is operated by a method including the steps of:
temporarily stopping the operation of the ultrafiltration unit to equalize a dialysate inflow rate into a dialyzer and a dialysate outflow rate from the dialyzer;
detecting a pressure of the dialysate, which is equal to the pressure in the blood flow line in the central part of the dialyzer, during every temporary stop of ultrafiltration; and
monitoring a fluctuation in the pressure of the dialysate as a fluctuation of a pressure of the blood.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only. However, it should be understood that the detailed description and specific example, while indicating preferred embodiments of a dialyzing system of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from the detailed description.